1. Field of the Invention
The present invention relates to a resonator device in which plural resonance modes are multiplexed, a method of producing the same, a filter, a composite filter device, a duplexer, and a communication device including the foregoing devices.
2. Description of the Related Art
Conventionally, cavity resonators and re-entrant cylindrical cavity resonators. (re-entrant resonators) have been used for operation at relatively high power in the microwave range. The re-entrant cylindrical cavity resonator is also called a coaxial cavity resonator. Its Q value is relatively high, and its size is smaller than that of a cavity resonator. Therefore, the use of re-entrant cylindrical cavity resonators has been effective in reducing the size of microwave filters.
On the other hand, with microcells being employed in cellular mobile communication systems, e.g., in mobile telephones and so forth, the need is growing to further reduce the size of filters for use in base stations.
To form a multistage resonator comprising a plurality of re-entrant cylindrical cavity resonators requires a number of resonators equal to the number of stages to be formed. Thus, there has been the problem that the overall size of the filter becomes large.
Accordingly, the present invention addresses this problem by providing a resonator device in which the structure of a re-entrant cylindrical cavity resonator or coaxial resonator is partially adopted, which can be configured in a small size, even when the number of resonator stages is increased.
The invention further provides a filter, a composite filter device, a duplexer, and a communication device using such a resonator.
To provide the above features, the resonator device in accordance with the present invention comprises a conductive rod provided in a conductive cavity with at least one end of the rod being electrically connected to the cavity, and a dielectric core provided in the cavity.
The mode of a re-entrant cylindrical cavity resonator is determined by the cavity and the conductor rod. A resonance mode such as a TM mode is determined by the cavity and the dielectric core. A resonance mode such as a TE mode is determined by the dielectric core. These resonance modes caused by use of the dielectric core and the mode of the above-mentioned re-entrant cylindrical cavity resonator are coupled to each other.
With this structure, resonators can be multiplexed in one cavity. By forming a single resonator device having a plurality of stages, the size of the device can be reduced.
Preferably, a hole is formed in the dielectric core, and the rod is inserted in and through the hole. With this structure, the dielectric core can be disposed in an optional position, e.g., in the center of the cavity.
The dielectric core may be bonded to the inner surface of the cavity. With this structure, the capacitance component which determines the resonance frequency in the resonance mode caused by the cavity and the dielectric core can be increased.
Preferably, the dielectric core is supported on a stand in the cavity, and the dielectric core is spaced from the inner surface of the cavity. With this structure, the capacitance component which determines the resonance frequency in the resonance mode caused by the dielectric core can be decreased.
Also preferably, the resonance modes caused by the cavity and the dielectric core provide a duplex TM mode, which is then coupled to the mode of the re-entrant cylindrical cavity resonator so as to provide a triplex mode.
A method of producing a resonator according to the present invention comprises the steps of selecting a material for the dielectric core such that the change of the resonance frequency in the resonance mode caused by the cavity and the dielectric core can be made substantially constant for changes in temperature, and selecting a material for the rod such that the change of the resonance frequency in the resonance mode caused by the cavity and the rod can be made substantially constant for changes in temperature.
In the filter of the present invention, an input-output conductor is provided in the resonator device having the above-described structure to be coupled to a predetermined mode of the above resonance modes in order to carry out input-output of a signal.
The composite filter device of the present invention comprises a plurality of the above-described filters.
The duplexer of the present invention comprises two sets of the filters, in which the input port of the first filter is an input port for a transmission signal, the output port of the second filter is an output port for a reception signal, and the input-output port shared by the first and second filters is an antenna port.
The communication device of the present invention is formed by use of the filter, the composite filter device, or the duplexer.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings, wherein like references indicate like elements and parts.